Method and apparatus for measuring mechanical properties of the respiratory system

ABSTRACT

Method and apparatus are disclosed for measuring respiratory resistance and stiffness by forcing a pulsating volume of gas at a known amplitude and frequency into and out of a respiratory system being examined, and sampling the gas pressure at the mouth of the patient in response to the pulsating volume at selected points in time when the rate of flow of the gas and volume displacement are peaked. Apparatus is disclosed for determining when such flow and displacement are peaked, and for converting the sampled pressures into direct readings of respiratory resistance and dynamic stiffness. Also, apparatus is disclosed for cancelling out of the sampled pressures values equal to residual pressure of the respiratory system by averaging the sampled pressure over at least two successive, alternate, sampling times.

United States Patent 1191 Hardway,Jr.

[ 1 Jan. 30, 1973 [54} METHOD AND APPARATUS FOR MEASURING MECHANICALPROPERTIES OF THE RESPIRATORY SYSTEM [75] Inventor: Edward V. Hardway,Jr., Houston,

Tex.

[73] Assignee: Spearhead, Inc., Houston, Tex. [22] Filed: Oct. 23, I970[21] Appl. No.: 83,421

52 u.s.c1 ..128/2.08

51 lnt.Cl. ..A6lb5/08 [58] FieldofSearch ..l28/2.08,2.07,2R,2S; 73/38,194, 231

[56] 6 References Cited UNITED STATES PATENTS 3,410,264 11/1968 Frederik..l28/2R 3,598,111 8/1971 K611116161. Mus/2.08

2,089,432 8/1937 Ryan ..73/38 FOREIGN PATENTS OR APPLICATIONS 192,3678/1967 U.S.S.R ..2.08/

1 V l l8 TMNSDUC E R PISTON AREA A 199,328 12/1967 u s.s.R ..L ..2.08

Primary ExaminerKyle L Howell Attorney-Hyer, Eickenroht, Thompson &Turner [57] ABSTRACT Method and apparatus are disclosed for measuringrespiratory resistance and stiffness by forcing a pulsating volume ofgas at a known amplitude and frequency into and out of a respiratorysystem being examined, and sampling the gas pressure at the mouth of thepatient in response to the pulsating volume at selected points in timewhen the rate of flow of the gas and volume displacement are peaked.Apparatus is disclosed for determining when such flow and displacementare peaked, and for converting the sampled pressures into directreadings of respiratory resistance and dynamic stiffness. Also,apparatus is disclosed for cancelling out of the sampled pressuresvalues equal to residual pressure of the respiratory system by averagingthe sampled pressure over at least two successive, alternate, samplingtimes.

PATENTEDJM 30 ms SHEET 1 BF 3 TMNSDUCER m f m 6 2 EDWARD 1/ /ABDWAYJR.

INVENTORf BY 6' I ZZ W KW A TTOENE Y5 METHOD ANDAPPARATUS FOR MEASURINGMECHANICAL PROPERTIES OF THE RESPIRATORY SYSTEM This invention relatesto methods and apparatus for physicological testing of the humanrespiratory system and in one of its aspects to such method andapparatus for measuring mechanical properties of the human respiratorysystem, such as total respiratory resistance and dynamic stiffness. Inanother aspect this invention relates to novel methods and apparatus formeasuring respiratory resistance and stiffness by forced oscillationtechniques.

Both the measurement of total respiratory resistance and dynamicstiffness of the respiratory system may be important in determining thecondition of the lung and the presence of related diseases. Themeasurement and indication of respiratory stiffness and of respiratorycompliance are considered equivalent since one is simply the reciprocalof the other. In measuring only total respiratory resistance of thehuman respiratory system, forced oscillation techniques are generallyemployed. One commercially available forced oscillation instrumentincludes a loudspeaker connected to a mouthpiece via a flow measuringpneumotach. The mouthpiece also connects through a long tube to theatmosphere to permit breathing. An alternating pressure at 3 Hz. iscreated by the loudspeaker and this pressure causes an alternating flowthrough the mouthpiece to and from the patients airway and lung. Thelevel of the alternating pressureat the mouthpiece is measured by apressure transducer. A differential pressure transducer is connectedacross the pneumotach, and an amplified electrical signal proportionalto the differential pressure across the pneumotach is obtained. Thecomponent of the measured alternating pressure proportional torespiratory resistance is the pressure at the instant of zero volumeacceleration, zero volume and peak flow with respect to the 3 Hz.oscillation. This point is determined by differentiating the electricalsignal and determining the point of zero volume acceleration with azerocrossover detector. The total respiratory resistance is then computed asthe ratio of the amplitude of the driving pressure at the instant ofpeak alternating flow to the amplitude of the induced peak alternatingflow.

The above described apparatus has severe limitations restricting itswidespread usage. The differential pressures which must be measuredacross the pneumotach to determine flow are extremely small, especiallywith a sick patient with high respiratory resistance. Two extremelysensitive pressure transducers are thus required. The linearpneumotachwith its multiplicity of small capillaries is easy to contaminate byphlegm and other breath particles. Also, a high performance recordermust be used to insure accuracy, and graphical or manual manipulationsare required to provide the desired result.

The change of stiffness or compliance of the human lung with breathingfrequency has been found by medical researchers to be closely related tothe degree of obstruction of the peripheral airways in the lungs.Presently known methods of determining respiratory stiffness involve theuse of a large and costly body plethysmograph or body box, and anesophageal balloon swallowed by the subject being tested. The bodyplethysmograph is so costly and the procedures em- It is another objectof this invention to provide such I methods and apparatus which do notemploy relatively expensive and complicated components such as apneumotach, differential pressure transducers, differentiating circuitryand zero crossover detectors.

It is another object of this invention to provide such methods andapparatus which are suitable both for laboratory use and for use inroutine medical examinations.

It is another object of this invention to provide such methods andapparatus wherein direct readings can be provided of respiratoryresistance and stiffness, even at different frequencies of appliedoscillations.

lt is another object of this invention to provide such methods andapparatus in which respiratory stiffness is measured without the need ofa body box or esophageal balloon swallowed by the subject.

lt is another object of this invention to provide such methods andapparatus in which the patient s breath can bezisolated from theapparatus to facilitate cleaning and disinfecting of the apparatusbetween successive patients.

It is another object of this invention to provide such methods andapparatus in which sampled pressures not generated in response to theforced oscillations are automatically cancelled.

These and other objects and advantages of this invention areaccomplished in accordance with this invention by providing a controlledvolume pump generating sinusoidal volume pulsations wherein both thevolume velocity or flow and the volume are precisely known andpredetermined with respect to amplitude, frequency and phase, making itunnecessary to differentiate the flow signal to determine the instantsof peak or zero flow. It is only necessary to sample the pressure levelsignal from a single transducer at known points of the oscillatoryvolume cycle to obtain the electrical signals necessary to determinerespiratory resistance and dynamic stiffness. The points of theoscillatory cycle where the sampled pressures are taken are preferablydetermined by indexing positions of a rotary driving mechanism drivingthe which positions are directly related to conditions of theoscillating volume. The indexed positions also have a fixed relationshipto resistive and reactive components of the sampled alternatingpressures. Circuit means are also provided so that these sampledpressures are converted to direct readings or recordings of respiratoryresistance or stiffness, and no graphical interpretation of anoscillating line on a graph is necessary. During these measurements, itis preferable for the patient to hold his breath for short periods, ashe would during the making of a Roentgenogram of his lungs. Means areprovided for cancelling errors due to linear and slow variations ofsignal level caused by voluntary or involuntary pressure used to isolatethe patient from the apparatus, thus greatly reducing the cleaning andsanitation problem.

In the drawings, wherein is illustrated a preferred embodiment of thisinvention, and wherein like reference numerals are used throughout todesignate like parts: 7 3

FIG. 1 is a schematic diagram of the apparatus of this invention andincludes an equivalent circuit or mechanical analogy of a respiratorysystem being tested;

FIG. 2 is a graph showing curves of alternating respiratory pressure atthe inlet to the respiratory system, and volume velocity or flow andvolume displacement of the oscillating volume;

FIG. 3 is a graph showing the pressure sampled at the inlet to therespiratory system at selected sampling times, superimposed on theresidual or baseline pressure of the respiratory system;

FIG. 4 is an overall schematic of the preferred form of the apparatus ofthis invention, including a partial sectional view of the controlledvolume pump and the limp diaphragm;

FIG. 5 is a more detailed schematic of the electrical circuits fordirect reading of respiratory resistance with the baseline pressurecancelled; 1

FIG. 6 is a schematic of one" form of the circuits for sampling thealternating pressure at the various sampling times of FIG. 3 to providethe input signals to the circuit of FIG. 5;

FIG. 7 is'a box chart showing the electrical potential stored in thevarious storage devices of FIG. 5 at different sampling times; and

FIG. 8 is a schematic diagram of a capacitor memory unit which is oneform of a switching circuit utilized in this invention to provide thestored values of FIG. 7 for readout of respiratory resistance lessbaseline pressure.

Referring to FIG. 1, a controlled volume pump 10 is shown as including apiston 11 driven in a constant sinusoidal motion by a scotch yoke 12.Scotch yoke 12 is connected between a piston rod 13 and a shaft 14 ofasynchronous rotary motor 15. Pump l0-is shown as being connected topump gas into and out of a respiratory system 16 represented inschematic form in FIG. ,1. Scotch yoke 12 converts the rotary motionofmotor 14 into reciprocating motion to reciprocate piston 11 from itscenter position 17 a maximum distance X alternately to positions 18 and19. Piston 11 moves at a constant frequency f determined by motor 14which has a constant angular velocity .w to provide a constant peakvolume V of gas which is forced into and out of the respiratory system.The rotary position of the shaft of motor 14 has a fixed relationshipwith respect to the position of piston 11 so that with each 360rotation'of the shaft piston 11 will move from its center position 17(represented by 0 rotation of the shaft) to position 18 (represented by90 rotation of the shaft) back to its center position 17 (nowrepresented by 180? rotation of the shaft) to position 19 (representedby 270 rotation of the shaft) and back to center position 17(represented by 360 rotation of the shaft). When piston 11 is in centerposition 17 the flow of gas into or out of system 16 is peaked; however,the volume V of gas is zero. Conversely, when piston 11 is in extremepositions 18 and 19, rate of flow V is zero and volume V is peakedeither in the positive direction at position 18 or the negativedirection at position 19. Thus, as long as the amplitude of the forcedvolume is constant the moments of peak flow or peak volume canbedetermined by the position of shaft 14.

In the mechanical analogy of respiratory system 16 in FIG. 1, gas ispumped into and out of the airways and lung through a mouthpiece orinlet 16a. At the levels of pressure and volume involved, gas may beconsidered incompressible. Thus, the total respiratory resistance R tothis flow is a combination of airway resistance, tissue resistance andthe resistance offered by the thoracic cage, all of which create backpressure com-ponents on the gas forced in by pump 10, which are in phasewith the oscillatory flow of gas. The respiratory stiffness S or itsreciprocal compliance C, analogous in action to a spring, offers a backpressure in phase with volume displacement. The inertial impedance ofthe respiratory system causes back pressure component 180 out of phasewith the stiffness component and is proportional to volume acceleration.However, at the low frequencies used inertial impedancemay be neglected.

Thus, by sampling the gas pressure at inlet 16a, such as by a transducer20, resistive and reactive components of pressure proportional torespiratory resistance R and stiffness S can be obtained. If thispressure is sampled when piston 11 is in center position l7,

R =-Pr/ V w (l) where Pr the pressure at 16a when V is peaked; V,

= the peaked value of the alternating volume .of

gas from pump 10 (being a fixed known value determined by the product ofthe area of piston 11 and X and w is angular velocity of motor 15 inradians per second.

Similarly, if the pressure at inlet 16a is sampled when piston l 1 is inone of positions 18 or 19, when volume is peaked, then the value of thealternating pressure Pa (hereinafter referred to as Ps) obtained will besubstantially proportional to dynamic stiffness S by the relationship: SPs/V (2) where P8 is the pressure at 16a when V is peaked, and V is theconstant peaked value of the alternating volume of gas.

The relationships of formulas l) and (2) are graphically illustrated inFIG. 2. Curve 23 represents the alternating pressures Pa induced by thealternating volume of gas from pump 10 and as measured by transducer 20'at inlet or mouthpiece 16a, and is plotted as a function of samplingtimes t -t corresponding to differentpositions of piston 11 and shaft14. Curve 24 represents the volume displacement of the alternatingvolume at times 2 4 and curve 25 represents the flow of the alternatingvolume of gas at times t If times t are selected at the zero crossoversof each of curves 24 and 25 and pressure Pa sampled at these times, thenthe values of Pr and Ps are respectively ob tained. Flow is peaked whenvolume is zero and vice versa.

Means are thus provided forsampling the alternating pressure Pa andindexing the relative positions of piston 11 corresponding to zerocrossover or peaks of curves 24 and 25. As illustrated schematically inFIG. 1, an indexing means such as rotary disk 26 can be connected toshaft 14 and connected to operate a switching or gate circuit 21. Forexample, disk 26 can be a rotary switch with terminals 90 apart or acollimator with slits 90 apart for passing light from light sources (notshown) on one side to a plurality of photocells (not shown) on the otherside which then emit pulses responding to each of the peaks or zerocrossovers of curves 24 and 25. Gate circuit 21 is also connected to theoutput of transducer 20 to provide an output at a terminal 22corresponding to the alternating pressure Pa sampled at each of times tSince the sampled value of Pa at the even numbered times t t t etc.,occur when V and \7 is peaked, then these values will be proportional torespiratory resistance R in accordance with formula (1). Similarly,since the sampled values of Pa at times t t t etc., occur when V ispeaked and \7 0, these sampled values will be proportional to dynamicstiffness in accordance with formula (2).

Since it is preferred that the patient hold his breath when utilizingthe present invention, the pressures sampled by transducer will includeresidual or baseline pressure Pb of the respiratory system. Such apressure is illustrated by line 27 in FIG. 3 having the sampledalternating pressure Pa superimposed on it by curve 23, and Pb maychange with time during successive sampling cycles t at a linear rate.In order to provide a direct reading of respiratory resistance andstiffness, novel sampling circuits and methods are provided by thisinvention to cancel the baseline pressures from the sampled pressuresduring each sampling cycle provided that this pressure is substantiallyconstant. A constant level of pressure Pb can be cancelled by averagingthe sampled pressures at successive, alternate, sampling times so that,for example, Pa /(P ,P or MP P,,). If Pb is changing in a linear manneras shown in FIG. 3, it is preferred to average at least two successivepairs of sampled pressures, with the end pressure of the first pairsampled being the first pressure of the second pair sampled. By thismethod the effect of a linearly changing baseline pressure is cancelled.In the present embodiment this is done by taking an average of threealternate sampled values (i.e., P P and P with double the intermediatesampled value being subtracted from the sum of the alternate sampledvalues on-each side of the intermediate sampled value. For example, twosuccessive, alternate positive peaks P and P would be added, and twicethe negative alternate intermediate peak P would be subtracted from thisto give the value of respiratory resistance less the linearly changingof baseline pressure. Using this method the equation for Pr, less Pbwould be (4n-+ n' PM" s)" 2PM 3)] The averaging and indicating processdescribed is done continuously although it may require up to two cyclesto stabilize the output.

FIG. 4 illustrates one embodiment of this invention in which Pb iscancelled and direct readings of R and S are provided by the methoddescribed. In this embodiment a pair of capacitor memory units 28R and288 are connected to shaft 14 of motor 15 by a gear 29R connected toshaft 30R of capacitor memory unit 28R, and a gear 298 connected toshaft 308 of capacitor memory unit 288. Gears 29R and 298 are driven byshaft 14 through a gear 31 connected to shaft 14 and gears 29R and 298are sized with respect to gear 31 to provide a 2l reduction so that foreach rotation of shaft 14,

shafts 30R and 308 are rotated 45. Each of capacitor memory units 28Rand 288 includes four rotary discs connected to their respective shafts,such as discs 32R, 33R, 34R and 35R in FIG. 8 each connected to shaft30R. For purposes of illustration, only the disc of capacitor memoryunit 28R are shown since the corresponding disc of capacitor memory unit28S are identical except that memory unit 285 runs ahead or lags behindmemory unit 28R by 45 corresponding to the 90 out of phase relationshipof curves 24 and 25. Each of discs 32R, 33R, 34R and 35R include eightterminals 45 apart which, also for purposes of illustration, are labeledwith the sampling times t t corresponding to when that terminal islocated at the position labeled B adjacent each of discs 32R-35R in FIG.8. Thus, discs 32R-35R in FIG. 8 are shown in the position they would bein at time t Disc 32R is connected between terminal M in the circuitryshown in FIG. 5, and ground and at times t and t conducts terminal M toground for reasons hereinafter described. Discs 33R and 34R areconnected through line 36a to pressure transducer 20 through anamplifier 36, disc 33R being connected between line 36a and terminals Xand Y of FIG. 5, and disc 34R being connected between line 36a andground. Disc 33R includes two storage capacitors C and C connectedtogether at one of their terminals at point A and connected at theirother terminals to opposite terminals t and t of disc 33R. Point A isalso connected to one terminal of a capacitor C mounted on disc 34R andcapacitor C is connected at its other terminal to terminals t and t ofdisc 34R. Disc 35R is connected between point A and ground, and conductspoint A to ground when terminals t,, t t t and t, are at point B.

' The output terminals X, Y and M of memory unit 28R are connected tothe input of a respiratory resistance readout circuit 37R, and theoutputs X, Y and M of memory units 288 are connected to a respiratorystiffness readout circuit 378, each connected to properly scaled meters38R and 38S to directly read respiratory resistance and stiffness. FIG.5 shows a preferred form of circuits 37R and 378 with circuit 37R beingspecifically shown; it being understood that the following descriptionalso applies to circuit 378. Circuit.

37R includes an input terminal X connected to the input of an amplifier39R which in turn is connected through a switching means such as relay40R to a storage device 56, which may be a capacitor storing signal Ex.An input terminal Y is similarly connected to the input of an amplifier41R which is in turn connected through relay 40R to a second storagedevice 57, which also may be a capacitor storing voltage Ey. The coil ofrelay 40R is connected to terminal M so that the contacts of relay 40Rmove from a normally open position to a closed position when terminal Mis grounded through disc 32R. The stored potentials in storage devices56 and 57 are combined through unity gain, high input impedanceamplifiers 42R and 43R and a voltage divider comprising resistors 44Rand 45R to provide a potential Ez, which is one-half the combined valuesof By and Ex. Potential Ez is conducted through a scaling resistor orpotentiometer 46R and a meter amplifier 47R to a meter 38R whichdirectly reads respiratory resistance.

It may be desirable to utilize different frequencies of forcedoscillations from pump 10 particularly where the apparatus is being usedas a laboratory instrument, and this can be done by changing the angularvelocity w of synchronous motor 15. Since angular velocity w is only afactor in determining total respiratory resistance (see Equations 1 and2) only the readout meter 38R for respiratory resistance need be scaledto reflect different frequencies of oscillation. The speed of motor 15could be a continuously variable D. C. motor or be switched betweendifferent speeds. For example, as shown in FIG. .4, motor 15 may be atwo speed sychronous motor operated at l r.p.s. and 2 r.p.s. and withthe switching between these speeds controlled by a two speed switch 48.As illustrated, switch 48 can also be connected to a relay 49 to switchin different values of scaling resistor 46 to permit meter 38R todirectly read respiratory resistance at both land 2 r.p.s. of motor 15.In the example given, the signal would be scaled to A for the higherspeed since it is necessary to scale the signal in inverse proportion tow.

FIG. 6 shows the equivalent circuits of capacitor memory unit 28R ateach of sampling times t -r and FIG. 7 shows the various potentials-Ex,By and Ez representing the sampled pressures Pa at sampling times t -tso that Equation (3) is satisfied. Using FIG. 3 as a reference, theelectrical value corresponding to pressure P is sampled and stored incapacitor C at time t theelectrical value corresponding to pressure P issampled and stored in capacitor C at time and the electrical valuecorresponding pressure P is sampled and stored in'capacitor C at time tAt time t the stored value corresponding to P is transfered to capacitor57 and at time the combined stored values corresponding to P -P and P -Pare transferred to capacitors 56 and 57 respectively where they arecombined and divided in half to provide Ez MP P, 2P This processcontinues through cycles t i when the electrical values nowcorresponding to P P and P are sampled, stored and combined.

If thedifference in phase relationship of curves 24 and 25 are takeninto account, then similar circuits could be drawn for illustrating theequivalent circuits of memory unit 28C at each of times t t forsatisfying Equation (4); it being understood that, for example, theequivalent circuit to t of FIG. 6 would appear at time t, for memoryunit 28C. Thus, where in the example shown the pressure Pa at times t tand t are respectively stored in capacitors C C and C of capacitormemory unit 28R, the pressure Pa at time t and would be respectivelystored in corresponding capacitors C C, and C (not shown) of memory unit28C.

Of course, other forms of switching and storage circuitsmay be utilizedby this invention to satisfy Equa each of the steps of sampling, storingand combining required, or since a constant angular velocity of motor isemployed only one position of shaft 14 corresponding to each positiveand negative peak of curve 23, need be indexed. Then the remaining stepscorresponding to those shown in FIG. 6 could be preformed under thecontrol of electronic timing circuits. For example, collimator 26 can bearranged so that separate light pulses are generated at timescorresponding to the positive peaks of each of curves 24 and 25, whichpulses are distinguishable from light pulses which are generated bycollimator 26 at times corresponding to each of the negative peaks ofthese curves. These pulses can then be used to trigger gate circuitsconnected between storage capacitors or other storage devicescorresponding to C,, C and C to load the sampled values of Pa into thesedevices at the appropriate sampling times, and to generate appropriatetiming pulses to trigger a switching circuit for combining the storedvalues.

Also, whether mechanical switching as shownin FIG. 8 or electronicswitching is employed, it may be desirable to provide a short delay inreadout at meters 38R and 388 until the sampling and combining of thevalues of Pa has-been stabilized, for example, after two full cycles ofthe alternating pressure Pa.

In order to protect pump 10 from being fouled by phlegm or mucus, a limpdiaphragm 50 assembly is preferably connected between pump 10 andmouthpiece 16a, as illustrated in FIG. 4. Assembly 50 includes a sealedhousing 51 preferably formed of two pieces hinged together at 52 andbolted together at 53 to permit easy opening and cleaning, and adiaphragm element 54 mounted in housing 50. Pressure transducer may beconnected to housing through an outlet 55 which may be mounted at theposition shown on the mouthpiece side of diaphragm element 54, as

shown in FIG. 4, or alternatively, on the pump side of diaphragm element54 when conditions are such that the pressures on each side of diaphragmelement 54 are substantially equal. Also, the pressure Pa may bedetermined at the sampling time without a separate pressure transducerby sampling the reaction force on piston 11, which will be proportionalto the pressure at inlet 16a, and converting this reaction force to anelectrical signal.

From the foregoing it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forth,together with other advantages which are obvious and which are inherentto the apparatus and methods disclosed.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims. 7

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterhereihset forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed is:

1-. Apparatus adapted for measuring mechanical properties of the humanrespiratory system comprising, in combination: pump means adapted forforcing a pulsating known volume of gas into and out of such arespiratory system at a known frequency, said pulsating volume of gasadapted to cause fluctuations in the gas pressure adjacent the inlet ofsuch a respiratory system when applied thereto; and inlet pressuresampling means adapted for sampling the gas pressure adjacent such aninlet, said sampling means responding to said pump means to sample saidgas pressure only at selected points in time during the time that saidpulsating volume of gas is applied to said respiratory system, saidsampling means including means adapted to sample the gas pressureadjacent such inlet at a plurality of first points in time during thetime that gas 'is being forced into and out of such a respiratorysystem, and second means adapted to sample such gas pressure at a secondplurality of selected points in time during the time that gas is beingforced into and out of such a respiratory system, said selected pointsin time being such that said sampled pressures are proportional to oneof respiratory resistance, or dynamic stiffness.

2. The apparatus of claim 1 wherein the sampled pressures at said inletinclude the residual pressure of the respiratory system, and whereinsaid sampling means includes means for effectively cancelling saidresidual pressure from the results obtained.

3. The apparatus of claim 1 further including respiratory resistanceelectrical readout means coupled to said sampling means and respondingto said sampled pressures proportional to respiratory resistance toprovide a visual readout of substantially the value of total respiratoryresistance of said respiratory system.

4. The apparatus of claim 3 wherein said electrical readout meansincludes means responding to the frequency of said pulsating volume ofgas to provide for a direct readout of said respiratory resistance atdifferent frequencies of said pulsating volume.

5. The apparatus of claim 1 further including respiratory stiffnesselectrical readout means coupled to said sampling means and respondingto said sampled pressures proportional to respiratory stiffness toprovide a visual readout of substantially the value of dynamic stiffnessof said respiratory system.

6. The apparatus of claim 1 further including a limp diaphragm adaptedto be connected between said pump means and such a respiratory system.7. Apparatus adapted for measuring mechanical properties of the humanrespiratory system comprising, in combination: pump means adaptedfor'forcing a pulsating known volume of gas into and out of such arespiratory system at a known frequency, said pulsating volume of gasadapted to cause fluctuations in the gas pressure adjacent the inlet ofsuch a respiratory system when applied thereto; and inlet pressuresampling means for sampling the gas pressure adjacent such an inlet,said sampling means including means responding to said puinpmeans tosample said gas pressure only at selected points in time during the timethat said pulsating volume of gas is applied to such a respiratorysystem, said selected points intime being such that saidsampledpressures are proportional to one of respiratory resistance, or,dynamic stiffness, and the sampled pressures at said inlet including theresidual pressure of the respiratory system, said sampling means furtherincluding means for effectively cancelling said residual ry resistanceor stiffness, and means responding to said separately stored sampledpressures to provide a pressure value substantially proportional to saidone of respiratory resistance or stiffness.

8. The apparatus of claim 7 wherein said means for separately storingsuccessive but alternate sampled pressures includes means for storingseparately the value of two successive positive sampled pressuresproportional to said one of respiratory resistance or stiffness, and thevalue of the intermediate negative sampled pressure proportional to saidone of respiratory resistance or stiffness, and wherein said meansresponding to said stored sampled pressures includes means for summingsaid successive positive sampled pressures and subtracting from this sumtwice the value of said intermediate negative peak of sampled pressures.

9. Apparatus adapted for measuring mechanical properties of the humanrespiratory system comprising, in combination: pump means adapted forforcing a pulsating known volume of gas into and out of such arespiratory system at a known frequency, said pulsating volume of gasadapted to cause fluctuations in the gas pressure adjacent the inlet ofsuch a respiratory system when applied thereto; rotary drive meansdrivingly connected to said pump means, the rotary position of saiddrive means having a fixed relationship to the flow and volumedisplacement of said gas; and inlet pressure sampling means for samplingthe gas pressure adjacent such an inlet, said sampling means respondingto said pump means to sample said gas pressure only at selected pointsin time during the time that said pulsating volume of gas is applied tosuch respiratory system, said selected points in time being such thatsaid sampled pressures are proportional to one of respiratoryresistance, or dynamic stiffness, said sampling means including indexingmeans responding to the rotary position of said drive means to providesaid selected points in time when said flow and volume displacement ofsaid gas are substantially peaked.

10. The apparatus of claim 9 wherein said sampling means includes meansproviding electrical values proportional to said sampled pressures atsaid selected points in time, and further includes storage meansresponding to said indexing means for separately storing such electricalvalues taken at at least two successive but alternate sampling times sothat each of said sampled pressures includes a pressure valueproportional to said one of respiratory resistance or stiffness, and apressure value corresponding to a residual pressure of the respirationsystem; and means responding to said separately stored electrical valuesfor combining said electrical values to provide another electrical valuesubstantially proportional to the value of said sampled pressures lesssaid residual 'pressures at said successive sampling times.

11. The apparatus of claim wherein said storage means includes aplurality of capacitors each for separately storing each of saidseparately stored electrical values, and said last-mentioned meansincludes switch means responding to said indexing means for selectivelystoring said separately stored electrical values in said capacitors andselectively combining said stored electrical values to provide acomposite electrical signal having a measurable electrical valueproportional to said one of respiratory resistance or stiffness.

12. The apparatus of claim 10 wherein said storage a respiratory systemat means and indexing means includes arotary capacitor memory unitdrivingly connected to said rotary drive means to follow the rotationthereof, said capacitor memory unit including a plurality of rotarydiscs driven by a common shaft and a plurality of storage capacitorsmounted on said disc and selectively connected during rotation of saiddisc to store separately at least three of said separately storedelectrical values, and wherein said last-mentioned means is connected tosaid capacitor memory unit and responds at selected times duringrotation of said capacitor memory unit to the stored electrical valuesin said storage capacitors to sum the first and third of said storedelectrical value and subtract from this sum twice the intermediatestored electrical value.

13. The apparatus of claim 12 including means whereby said first andthird of said stored electrical values are proportional to positivepeaks of the sampled alternating pressure proportional to respiratoryresistance, and the intermediate stored electrical value is proportionalto. the negative peak of the sampled alternating pressure intermediatesaid first and third peaks and proportional to respiratory resistance.

14. The apparatus of claim 12 including means whereby said first andthird of said stored electrical values are proportional to positivepeaks of the sampled alternating pressure proportional to respiratorystiffness, and the intermediate stored electrical value is proportionalto the negative peak of the sampled alternating pressure intermediatesaid first and third peaks and proportional to respiratory stiffness.

15. A method of determining mechanical properties of thehumanrespiratory system, including respiratory resistance and stiffnessin such a respiratory system, said method comprising the steps of:forcing a pulsating predetermined volume of gas into and out of saidrespiratory system at a known frequency, said pulsating volume causingfluctuations in the gas pressure adjacent the inlet to said respiratorysystem; sampling the gas pressure adjacent said inlet in response tosaid pulsating volume of gas at selected'points in time to determineresistive and reactive components of said pressure respectivelyproportional to respiratory resistance and stiffness, said sampling stepincluding the steps of determining a plurality of first points in timeduring the time that gas is being forced into and out of such arespiratory system when the flow of said gas is substantially peaked,sampling the inletgas pressures of said said first points in time, saidsampled pressures being substantially proportional to total respiratoryresistance, determining a plurality of second points in time during thetime that gas is being forced into and out of such a respiratory systemwhen the volume displacement of said gas is substantially peaked, andsampling the inlet gas pressures of said respiratory system at saidsecond points in time, said sampled pressures being substantiallyproportional to dynamic respiratory stiffness; and utilizing at least apart of said sampled pressures to obtain measurable indicationsproportional to total respiratory resistance and stiffness of saidrespiratory system.

16. The method of claim 15 wherein a constant rotary motion is utilizedto force said known volume into and out of said respiratory system, andsaid first and second points in time are determined by indexing saidrotary motion.

17. The method of claim 16 wherein said sampled pressures include valuesequal to residual pressures of the respiratory system, and furtherincluding the step of cancelling said residual pressure from saidmeasurable indication.

18. The method of claim 17 wherein said cancelling step includes thesteps of averaging the values of successive, sampled pressuresproportional to one of respiratory resistance orstiffness.

19. The method of claim 18 wherein said averaging step includes thesteps of separately storing the values .of three successive sampledpressures proportional to said one of respiratory resistance orstiffness, combining the first and third of said stored values, andsubtracting from this sum twice the intermediate stored value.

1. Apparatus adapted for measuring mechanical properties of the humanrespiratory system comprising, in combination: pump means adapted forforcing a pulsating known volume of gas into and out of such arespiratory system at a known frequency, said pulsating volume of gasadapted to cause fluctuations in the gas pressure adjacent the inlet ofsuch a respiratory system when applied thereto; and inlet pressuresampling means adapted for sampling the gas pressure adjacent such aninlet, said sampling means responding to said pump means to sample saidgas pressure only at selected points in time during the time that saidpulsating volume of gas is applied to said respiratory system, saidsampling means including means adapted to sample the gas pressureadjacent such inlet at a plurality of first points in time during thetime that gas is being forced into and out of such a respiratory system,and second means adapted to sample such gas pressure at a secondplurality of selected points in time during the time that gas is beingforced into and out of such a respiratory system, said selected pointsin time being such that said sampled pressures are proportional to oneof respiratory resistance, or dynamic stiffness.
 1. Apparatus adaptedfor measuring mechanical properties of the human respiratory systemcomprising, in combination: pump means adapted for forcing a pulsatingknown volume of gas into and out of such a respiratory system at a knownfrequency, said pulsating volume of gas adapted to cause fluctuations inthe gas pressure adjacent the inlet of such a respiratory system whenapplied thereto; and inlet pressure sampling means adapted for samplingthe gas pressure adjacent such an inlet, said sampling means respondingto said pump means to sample said gas pressure only at selected pointsin time during the time that said pulsating volume of gas is applied tosaid respiratory system, said sampling means including means adapted tosample the gas pressure adjacent such inlet at a plurality of firstpoints in time during the time that gas is being forced into and out ofsuch a respiratory system, and second means adapted to sample such gaspressure at a second plurality of selected points in time during thetime that gas is being forced into and out of such a respiratory system,said selected points in time being such that said sampled pressures areproportional to one of respiratory resistance, or dynamic stiffness. 2.The apparatus of claim 1 wherein the sampled pressures at said inletinclude the residual pressure of the respiratory system, and whereinsaid sampling means includes means for effectively cancelling saidresidual pressure from the results obtained.
 3. The apparatus of claim 1further including respiratory resistance electrical readout meansCoupled to said sampling means and responding to said sampled pressuresproportional to respiratory resistance to provide a visual readout ofsubstantially the value of total respiratory resistance of saidrespiratory system.
 4. The apparatus of claim 3 wherein said electricalreadout means includes means responding to the frequency of saidpulsating volume of gas to provide for a direct readout of saidrespiratory resistance at different frequencies of said pulsatingvolume.
 5. The apparatus of claim 1 further including respiratorystiffness electrical readout means coupled to said sampling means andresponding to said sampled pressures proportional to respiratorystiffness to provide a visual readout of substantially the value ofdynamic stiffness of said respiratory system.
 6. The apparatus of claim1 further including a limp diaphragm adapted to be connected betweensaid pump means and such a respiratory system.
 7. Apparatus adapted formeasuring mechanical properties of the human respiratory systemcomprising, in combination: pump means adapted for forcing a pulsatingknown volume of gas into and out of such a respiratory system at a knownfrequency, said pulsating volume of gas adapted to cause fluctuations inthe gas pressure adjacent the inlet of such a respiratory system whenapplied thereto; and inlet pressure sampling means for sampling the gaspressure adjacent such an inlet, said sampling means including meansresponding to said pump means to sample said gas pressure only atselected points in time during the time that said pulsating volume ofgas is applied to such a respiratory system, said selected points intime being such that said sampled pressures are proportional to one ofrespiratory resistance, or dynamic stiffness, and the sampled pressuresat said inlet including the residual pressure of the respiratory system,said sampling means further including means for effectively cancellingsaid residual pressure from the results obtained, said last mentionedmeans including storage means for separately storing values of saidsampled pressures taken at at least two successive but alternatesampling times when said sampled pressures are proportional to one ofsaid respiratory resistance or stiffness, and means responding to saidseparately stored sampled pressures to provide a pressure valuesubstantially proportional to said one of respiratory resistance orstiffness.
 8. The apparatus of claim 7 wherein said means for separatelystoring successive but alternate sampled pressures includes means forstoring separately the value of two successive positive sampledpressures proportional to said one of respiratory resistance orstiffness, and the value of the intermediate negative sampled pressureproportional to said one of respiratory resistance or stiffness, andwherein said means responding to said stored sampled pressures includesmeans for summing said successive positive sampled pressures andsubtracting from this sum twice the value of said intermediate negativepeak of sampled pressures.
 9. Apparatus adapted for measuring mechanicalproperties of the human respiratory system comprising, in combination:pump means adapted for forcing a pulsating known volume of gas into andout of such a respiratory system at a known frequency, said pulsatingvolume of gas adapted to cause fluctuations in the gas pressure adjacentthe inlet of such a respiratory system when applied thereto; rotarydrive means drivingly connected to said pump means, the rotary positionof said drive means having a fixed relationship to the flow and volumedisplacement of said gas; and inlet pressure sampling means for samplingthe gas pressure adjacent such an inlet, said sampling means respondingto said pump means to sample said gas pressure only at selected pointsin time during the time that said pulsating volume of gas is applied tosuch respiratory system, said selected points in time being such thatsaid sampled pressures are proportional to one of respiratoryresistAnce, or dynamic stiffness, said sampling means including indexingmeans responding to the rotary position of said drive means to providesaid selected points in time when said flow and volume displacement ofsaid gas are substantially peaked.
 10. The apparatus of claim 9 whereinsaid sampling means includes means providing electrical valuesproportional to said sampled pressures at said selected points in time,and further includes storage means responding to said indexing means forseparately storing such electrical values taken at at least twosuccessive but alternate sampling times so that each of said sampledpressures includes a pressure value proportional to said one ofrespiratory resistance or stiffness, and a pressure value correspondingto a residual pressure of the respiration system; and means respondingto said separately stored electrical values for combining saidelectrical values to provide another electrical value substantiallyproportional to the value of said sampled pressures less said residualpressures at said successive sampling times.
 11. The apparatus of claim10 wherein said storage means includes a plurality of capacitors eachfor separately storing each of said separately stored electrical values,and said last-mentioned means includes switch means responding to saidindexing means for selectively storing said separately stored electricalvalues in said capacitors and selectively combining said storedelectrical values to provide a composite electrical signal having ameasurable electrical value proportional to said one of respiratoryresistance or stiffness.
 12. The apparatus of claim 10 wherein saidstorage means and indexing means includes a rotary capacitor memory unitdrivingly connected to said rotary drive means to follow the rotationthereof, said capacitor memory unit including a plurality of rotarydiscs driven by a common shaft and a plurality of storage capacitorsmounted on said disc and selectively connected during rotation of saiddisc to store separately at least three of said separately storedelectrical values, and wherein said last-mentioned means is connected tosaid capacitor memory unit and responds at selected times duringrotation of said capacitor memory unit to the stored electrical valuesin said storage capacitors to sum the first and third of said storedelectrical value and subtract from this sum twice the intermediatestored electrical value.
 13. The apparatus of claim 12 including meanswhereby said first and third of said stored electrical values areproportional to positive peaks of the sampled alternating pressureproportional to respiratory resistance, and the intermediate storedelectrical value is proportional to the negative peak of the sampledalternating pressure intermediate said first and third peaks andproportional to respiratory resistance.
 14. The apparatus of claim 12including means whereby said first and third of said stored electricalvalues are proportional to positive peaks of the sampled alternatingpressure proportional to respiratory stiffness, and the intermediatestored electrical value is proportional to the negative peak of thesampled alternating pressure intermediate said first and third peaks andproportional to respiratory stiffness.
 15. A method of determiningmechanical properties of the human respiratory system, includingrespiratory resistance and stiffness in such a respiratory system, saidmethod comprising the steps of: forcing a pulsating predetermined volumeof gas into and out of said respiratory system at a known frequency,said pulsating volume causing fluctuations in the gas pressure adjacentthe inlet to said respiratory system; sampling the gas pressure adjacentsaid inlet in response to said pulsating volume of gas at selectedpoints in time to determine resistive and reactive components of saidpressure respectively proportional to respiratory resistance andstiffness, said sampling step including the steps of determining aplurality of first points in time during the time that gas is beingforced into and out of such a respiratory system when the flow of saidgas is substantially peaked, sampling the inlet gas pressures of saidrespiratory system at said first points in time, said sampled pressuresbeing substantially proportional to total respiratory resistance,determining a plurality of second points in time during the time thatgas is being forced into and out of such a respiratory system when thevolume displacement of said gas is substantially peaked, and samplingthe inlet gas pressures of said respiratory system at said second pointsin time, said sampled pressures being substantially proportional todynamic respiratory stiffness; and utilizing at least a part of saidsampled pressures to obtain measurable indications proportional to totalrespiratory resistance and stiffness of said respiratory system.
 16. Themethod of claim 15 wherein a constant rotary motion is utilized to forcesaid known volume into and out of said respiratory system, and saidfirst and second points in time are determined by indexing said rotarymotion.
 17. The method of claim 16 wherein said sampled pressuresinclude values equal to residual pressures of the respiratory system,and further including the step of cancelling said residual pressure fromsaid measurable indication.
 18. The method of claim 17 wherein saidcancelling step includes the steps of averaging the values ofsuccessive, sampled pressures proportional to one of respiratoryresistance or stiffness.